(Left) pH-responsive gel particles (red) being internalized by dendritic cells (green), key immune sentinels that regulate the initiation of immune responses.  (Right) Cartoon representation of “striped” gold nanoparticles, each ~10 nm in diameter and coated with an organized rippled nanostructure presenting hydrophilic sulfonate and hydrophobic methyl groups.  These particles are capable of penetrating the external membrane of cells, entering the cytosol without toxicity or disruption of the integrity of the plasma membrane.  These particles may provide a new way to efficiently deliver drugs or diagnostic agents into cells.